The prior art has recognized the utility of inert particulate solids as insecticides, see for example; Driggers, B. F., "Experiments with Talc and Other Dusts Used Against Recently Hatched Larvae of the Oriental and Codling Moths", J. Econ. Ent. 22 327-334 (1929); Hunt, C. R., "Toxicity of Insecticide Dust Diluents and Carriers to Larvae of the Mexican Bean Beetle", J. Econ. Ent. 40 215-219 (1947); and U.S. Pat. No. 3,159,536 (1964), each of which is incorporated herein by reference.
These references all describe applying particulate solids to foliage or insects by dry dusting. Although dry dusting is useful for laboratory experimentation it is not applicable for large scale agricultural use. The use of dry dusting has declined because the extremely fine particles, usually on the order of less than 30 um, with a median particle size typically between 0.5 to 3.0 um, are prone to drift and therefore have high negative environmental impact. Dry particles also do not adhere well to the target substrate (e.g. plants). Typically only 10% to 20% of the dry dust is deposited onto the target. (Pesticide Application Methods by G. A. Mathews Longman Scientific & Technical, Second Ed. (1992).)
It has also been determined that hydrophobic particulate solids can be applied to substrates as a liquid composition to form a hydrophilic coating. To this end, the particulate substances have been combined with a dispersant having a hydrophilic end and a lipophilic end and the same added to water to form an aqueous dispersion. The dispersant concentrates at an interphase between the hydrophobic substance and water with the lipophilic end of the dispersant positioned toward the hydrophobic substance and the hydrophilic end toward the water.
General classes of dispersants are divided into different groups by chemical functionality, e.g., cationic, anionic, amphoteric, nonionic. Typical examples of surfactants include soaps (carboxylate salts), sulfonates, sulfated alcohol ethoxylates, alkylphenol ethoxylates, carboxylic and polyoxyethylene esters, amines, imidazolines, and quaternary ammonium salts. Extensive lists containing hundreds of commercial dispersants are readily available (see McCutcheon's Emulsifiers & Detergents N. Amer Ed. (1995)).
The use of dispersants, however, causes the particulate hydrophobic substance to become hydrophilic and to retain this hydrophilic character after drying. Therefore, when such dispersions are placed on a substrate they will retain water. Water results in surface damage to many substrates including agricultural crops and other plants (disease), lumber (rot), concrete (freeze cracking), soil (erosion), textiles, solid chemicals such as fertilizers (leach), and the like. Accordingly, the use of dispersants for employing a dispersion of hydrophobic particulate solids for protecting surfaces has been problematical.
It would therefore be a significant advance in the art of applying hydrophobic particulate solids to a substrate to provide the substrate with a continuous film of the particulate solid while retaining a hydrophobic character. The resulting film would provide a substantial deterrent to damage due to water.